idle problem (exhaust?)

[Uberck]

1993 s13 w/ 105xxx miles and am having a minor problem. around 6-700 rpms the car shakes violently, but once i rev it up past 1.5k the shaking stops. im thinking a puncture in my exhaust system because revving it up i can hear the rev skipping beats. i dont know if that makes sense you have to be there to hear it. any other suggestions?